The two key elements of flash flooding are rainfall intensity and how long the rain lasts. Topography, soil conditions and ground cover play critical roles, as well.

Because our land is so dry, there is a hard crust over it which makes it difficult for the ground to absorb moisture. When water cannot seep into the ground, it runs off and collects in our low lying roads and washes leading to flooding.

The Federal Emergency Management Agency, FEMA, compiles detailed mapping of areas that have "a one percent chance to be equaled or exceeded in any year," which they deem the 100-year floodplains map. In other words, this map depicts areas that see flooding and have a chance for excessive flooding.

Flood insurance discounts:

The City of Phoenix just announced Wednesday that Phoenix owners can now get an addition 5 percent discount on flood insurance thanks to a new FEMA designation. Previously those in "high-risk flooding areas" in Phoenix could get a 20 percent discount on flood insurance. That discount is now being raised to 25 percent. To see if you qualify, visit www.floodsnart.gov.

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Take a look at the FEMA floodplain map below. The red lines comprise the currently defined floodplains areas in the Valley.